This type of actuation for a control valve has been disclosed by German Patent Publication No. 2,012,000. With this type of actuation arrangement, as with other actuations, the area of the flow cross-section does not uniformly correspond to the travel of the actuation unit, but rather the cross-section of the opening progressively increases at a uniform opening rate or at a steadily increasing valve opening travel. This is undesirable, especially when the control valve is used to control a cold air flow and a hot air flow for mixed-air heating, and the goal is linear control of the mixed air. According to German Pat. No. 2,504,475, linear control of the mixed air can be obtained by coupling to the free end of the control valve a scoop-shaped part which leads or lags behind the movement of the control valve. However, this type of arrangement is relatively complex.